Organization- Novel-Only Monsters

He laughed then, high and hysterical, and the elevator started moving again. Another vaguely lit blank metal wall, and then the light from behind them changed. He and Dana turned together to see a second identical elevator revealed. This one contained a grotesque alien, straight out of the movie, all sickly suckers and flailing limbs. It leapt at the glass and stuck there, its grotesquely sexual mouth sliming and sucking as it tried to probe at them, impregnate them, and then they moved on again, descending before jerking to the side once more.
...

And it was like that, arms wound around each other, sharing the warmth of their bodies and the pain of their wounds, that they emerged into a huge underground space like a warehouse where countless elevators shifted left and right, up and down, running on almost invisible rails and columns and passing soundlessly across junctions, swapping position constantly. In each elevator was something of shade or light, and whether dark or light, it was always horrible.

Vampires, not of the limp, fluffy-collared variety, but with pale skin and too many teeth. Three people—two adults and a child—with horribly cracked, blistered skin, beneath which lava seemed to boil. A gorgeous naked woman with teeth in place of a vagina. A man with six arms, each of the hands replaced with a grafted weapon of some kind, from a knife to a shotgun. A screaming banshee with hair flowing around its head as if in slow motion.

Six elevators contained small babies that seemed to explode again and again, scattering bladed blood-red shards. A giant rabbit with oversized teeth, a woman with a scorpion’s sting curved from the small of her back, a child with three heads—vampire, zombie, werewolf—a shade of something terrible, a ghostly figure surrounded by fumes that must be toxic, a minotaur with a monstrous phallus, a woman with writhing snakes instead of pubic hair, a man with steaming pipes inserted into his chest and flames in his eyes, a dog with the head of an alligator…

The horrors were endless and almost beyond imagining, and Marty and Dana held each other tighter as their elevator was carried through the impossible space.

- The Cabin in the Woods: The Official Movie Novelization, chapter 10